In a process for fabricating a semiconductor structure, layers, for example, comprising integrated circuits may be transferred. Such transfers especially allow circuits to be attached to substrates other than those used to produce them, or else allow circuits to be stacked so as to form “3D” components.
If the thin layer to be transferred is of a small thickness (i.e., below 200 μm), it may, during transfer, be liable to crack or split or, more generally, it may be damaged.
A solution disclosed in EP 0,786,801 for reinforcing the layer to be transferred or the substrate to be treated comprises temporarily bonding a handle substrate to the substrate comprising the layer to be transferred. The layer to be transferred or the substrate to be treated may thus be freely handled and undergo all the fabrication steps necessary for its transfer or treatment.
In EP 0,786,801, the handle substrate comprises a cleavage zone that allows, at the end of the process, the handle substrate to be removed along this cleavage zone.
One problem is that such a handle substrate consumes material. Furthermore, it is not easy to recycle the remaining part in order to reuse it. This is because it is necessary to implement a polishing operation, thereby increasing the duration and cost of the process.
Another known solution, which does not consume material, consists in temporarily bonding, by means of an adhesive, the handle substrate to the substrate comprising the layer to be transferred.
In this case, during the transfer or treatment, the force associated with the attachment of the layer to be transferred and the handle substrate is withstood by the adhesive.
Once the transfer or treatment has been carried out, the handle substrate may be removed.
A problem arises from the use of an adhesive.
This is because adhesives can become unstable if exposed to the high temperatures employed in the treatments carried out on the substrate or during fabrication of semiconductor structures using a transfer.
Moreover, an adhesive layer does not allow sufficiently stable attachment of the substrate for certain treatments to be carried out thereon. This is the case when the substrate, for example, is thinned by grinding to below a thickness threshold, for example, of 200, 50 or 40 microns. The mechanical stress exerted in this step leads to strain in the layer resting on the insufficiently rigid adhesive layer, thereby, in turn, leading to non-uniform thinning of the substrate.
Furthermore, once the treatment has been carried out, the adhesive is completely removed by means of a chemical removal technique (dissolving in a solvent, for example). Such removal increases the duration of the fabrication process and risks damaging the semiconductor structure obtained.